Low Salt Intake and Changes in Serum Sodium Levels in the Combination Therapy of Low-Dose Hydrochlorothiazide and Angiotensin II Receptor Blocker

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Background: The present study was conducted to examine the association of dietary salt intake with changes in serum sodium (srNa) levels when angiotensin II receptor blocker (ARB) treatment is changed to the combination of ARB plus low-dose diuretic (hydrochlorothiazide [HCTZ]). Methods and Results: In 88 patients (age 70±12 years), ARB treatment was switched to the combination therapy (same dosage ARB+12.5mg/day HCTZ). The srNa level was measured before and 6 months after administration of the combination. The daily salt intake was estimated by the Kawasaki formula using second morning urine sample. The study subjects were divided into quintile ranges according to daily salt intake. The reduction in srNa levels by switching to the combination treatment was significant in subjects in the lowest quintile Q5 (≤8.9g/day salt intake), but not in those in Q1–4 (28.1–9.3g/day salt intake). Increases in serum creatinine and uric acid levels were significantly larger in the former group than in the latter group. Conclusions: In elderly Japanese subjects with low salt intake (<8.9g/day), the addition of a low-dose diuretic (12.5mg HCTZ) to ARB treatment causes significant reduction in srNa levels, which might affect blood osmolarity.